The present invention relates to semiconductor devices having gate insulating films made of a high dielectric constant material, and to methods for fabricating the same.
With recent advances in techniques for enabling increased degrees of integration in and high-speed operation of semiconductor devices, MOSFETs (metal oxide semiconductor field effect transistors) have decreased in size. Along with this decrease in MOSFET size, gate insulating films have become progressively thinner, and as a result, the problem of enlarged gate leakage current due to tunnel current has become manifest. To address the problem, techniques have been studied for realizing a gate insulating film having a capacity equivalent to that of a thin SiO2 film (that is, a small equivalent oxide (SiO2) thickness, hereinafter referred to as xe2x80x9cEOTxe2x80x9d) and having a large physical film thickness (meaning a small leakage current), by using, as a material for the gate insulating film, a high-k material having a dielectric constant higher than that of SiO2 (hereinafter referred to as a xe2x80x9chigh-dielectric-constant materialxe2x80x9d). Specific examples of such a high-dielectric-constant material include an insulating metal oxide such as HfO2 or ZrO2.
In addition, lately, multi-function circuits, such as internal circuits for performing computational operations, peripheral circuits for carrying out input and output, and DRAMs (dynamic random access memories), have been generally integrated on a single chip set out as a system LSI. As components of such a system LSI, MOSFETs that, in accordance with their functions, have enhanced driving power even though their leakage current is large, or have decreased leakage current even though their driving power is low are being sought. Being used in this regard is technology by which the SiO2 films that serve as gate insulating films in MOSFETs are varied in thickness on the basis of the MOSFET functions,xe2x80x94specifically, multi-gate insulating film technology for forming gate insulating films with differing thicknesses.
When a high-dielectric-constant material is used as a material for a gate insulating film, however, it is difficult to obtain a desired EOT even though increase in the gate leakage current can be prevented.
Further, there is also a problem with the multi-gate insulating film technology, in that the gate leakage current is increased owing to the small thickness of the gate insulating films.
In view of the foregoing, a first object of the present invention is to realize a gate insulating film with small EOT and small leakage current, and a second object thereof is to prevent increase in gate leakage current when multi-gate insulating film technology is used.
To achieve the objects, the present inventors investigated the cause of the failure to realize a desired EOT even when a high-dielectric-constant material (specifically, a metal oxide) is used as a material for a gate insulating film, and the following has been made clear.
Specifically, when a metal oxide layer which serves as a gate insulating film is formed on a silicon substrate, an insulating compound layer (hereinafter, referred to as a xe2x80x9cmetal silicate layer) made of the three elements of silicon, oxygen and a metal contained in the metal oxide layer forms between the silicon substrate and the metal oxide layer. In other words, a gate insulating film is formed out of the multilayer structure of the metal silicate layer and the metal oxide layer. In this case, the dielectric constant of the metal silicate layer is lower than the dielectric constant of the metal oxide layer, thus decreasing the effective dielectric constant of the entire gate insulating film. As a result, a gate insulating film having a desired EOT cannot be formed, and therefore a MOSFET having such high driving power as expected cannot be realized, that is, the performance of the MOSFET cannot be enhanced.
FIG. 6 is a cross-sectional view illustrating a known semiconductor device, specifically a known MOSFET in which zirconium oxide (ZrO2) is used as a high-dielectric-constant material constituting a gate insulating film.
As shown in FIG. 6, a zirconium oxide layer 11, which serves as a gate insulating film, is formed on a silicon substrate 10. At this time, however, a zirconium silicate layer 12 forms between the silicon substrate 10 and the zirconium oxide layer 11. Accordingly, a gate electrode 13 will be formed on the gate insulating film made of the multilayer structure of the zirconium oxide layer 11 and the zirconium silicate layer 12.
Meanwhile, the present inventors found that when a metal oxide layer, which acts as a high-dielectric-constant material layer, is formed on a silicon substrate by, e.g., reactive sputtering, a metal silicate layer having a uniform thickness of about 2 through 3 nm and having a dielectric constant higher than the dielectric constant of a SiO2 film can be formed between the silicon substrate and the metal oxide layer by controlling particles sputtered from the target and implanted into the substrate surface, or by controlling the O2 plasma generated during the sputtering. They also found that by using the metal silicate layer as a gate insulating film, that is, by forming the metal oxide layer and the metal silicate layer and subsequently removing the metal oxide layer, the first object can be achieved, that is, a gate insulating film with small EOT and small leakage current can be realized. Note that when chemical vapor deposition, for example, is used instead of the reactive sputtering to form a metal silicate layer, such a quality metal silicate layer as mentioned above can also be formed.
The present inventors also found the following. When another metal oxide layer is formed on the metal silicate layer after the metal oxide layer has been removed, said another metal oxide layer can be formed as designed without taking reaction with the substrate into account; thus by using the multilayer structure of the metal silicate layer and said another metal oxide layer as a gate insulating film, the first object can also be achieved.
The present inventors further found that by forming a metal oxide layer and a metal silicate layer, and then partially removing the metal oxide layer, multi-gate insulating film technology in which the single layer structure of the metal silicate layer is used as a thin gate insulating film and the multilayer structure of the metal silicate layer and the metal oxide layer is used as a thick gate insulating film can be realized. This enables the second object to be achieved, that is, the gate leakage current can be controlled when the multi-gate insulating film technology is used. In this case, the multilayer structure of the metal silicate layer and another metal oxide layer may also be used as a thin gate insulating film.
The present invention was made based on the above-described findings. Specifically, in order to achieve the first object, a first inventive method for fabricating a semiconductor device includes the steps of: (a) forming a metal silicate layer containing at least a first metal on a silicon substrate, and also forming a metal oxide layer containing the first metal on the metal silicate layer; (b) removing the metal oxide layer, thereby forming a gate insulating film made of the metal silicate layer; and (c) forming a gate electrode on the gate insulating film.
According to the first inventive method for fabricating a semiconductor device, a metal silicate layer and a metal oxide layer both containing a first metal are sequentially formed on a silicon substrate, and the metal oxide layer is then removed, thereby forming a gate insulating film made of the metal silicate layer. In this method, a metal silicate layer with a uniform thickness and a dielectric constant higher than that of SiO2 can be formed by a reactive sputtering method or by a chemical vapor deposition method, for example, and the thickness of the metal silicate layer can be easily adjusted by controlling the sputtering conditions or the deposition conditions, for example. Accordingly, it is possible to obtain a gate insulating film with small EOT and small leakage current, enabling realizing a low-power-consumption MOSFET having desired driving power.
In order to achieve the first object, a second inventive method for fabricating a semiconductor device includes the steps of: (a) forming a metal silicate layer containing at least a first metal on a silicon substrate, and also forming a metal oxide layer containing the first metal on the metal silicate layer; (b) removing the metal oxide layer, and then forming another metal oxide layer containing a second metal different from the first metal over the silicon substrate, thereby forming a gate insulating film made of the metal silicate layer and said another metal oxide layer; and (c) forming a gate electrode on the gate insulating film.
According to the second inventive method for fabricating a semiconductor device, a metal silicate layer and a metal oxide layer both containing a first metal are sequentially formed on a silicon substrate, the metal oxide layer is then removed, and thereafter another metal oxide layer containing a second metal different form the first metal is formed, thereby forming a gate insulating film made of the metal silicate layer and said another metal oxide layer. In this method, a metal silicate layer with a uniform thickness and a dielectric constant higher than that of SiO2 can be formed by a reactive sputtering method or by a chemical vapor deposition method, for example, and the thickness of the metal silicate layer can be easily adjusted by controlling the sputtering conditions or the deposition conditions, for example. Further, since said another metal oxide layer is separately formed on the metal silicate layer, said another metal oxide layer can be formed as designed without taking reaction with the silicon substrate into account. Accordingly, with the multilayer structure of the metal silicate layer and said another metal oxide layer, a gate insulating film with small EOT and small leakage current can be realized, which enables realizing a low-power-consumption MOSFET having desired driving power.
Moreover, according to the second inventive method for fabricating a semiconductor device, the multilayer structure of the metal silicate layer and said another metal oxide layer can be easily formed to have a desired thickness configuration. This enables the design of a gate insulating film in accordance with the functions called for in a MOSFET. For example, designing a gate insulating film targeted at compatibility between high driving power and lower power consumption is facilitated.
Furthermore, in the second inventive method for fabricating a semiconductor device, the first metal is preferably selected in such a manner that the metal silicate layer is thermally stable at the interface with the substrate and does not cause creation of great strain in the silicon crystal, which would result in deterioration of mobility in the silicon crystal. In addition, the second metal is preferably selected in such a manner that the dielectric constant of said another metal oxide layer containing the second metal is higher than the dielectric constant of the metal oxide layer containing the first metal.
In order to achieve the second object, a third inventive method for fabricating a semiconductor device includes the steps of: (a) forming a metal silicate layer containing at least a first metal in a first device-formation region and a second device-formation region on a silicon substrate, and also forming a metal oxide layer containing the first metal on the metal silicate layer; (b) removing part of the metal oxide layer located in the first device-formation region, thereby forming a first gate insulating film made of the metal silicate layer in the first device-formation region, and also forming a second gate insulating film made of the metal silicate layer and the metal oxide layer in the second device-formation region; and (c) forming a first gate electrode on the first gate insulating film, and also forming a second gate electrode on the second gate insulating film.
According to the third inventive method for fabricating a semiconductor device, a metal silicate layer and a metal oxide layer both containing a first metal are sequentially formed on a silicon substrate, and the metal oxide layer is then partially removed, thereby forming a first gate insulating film made of the metal silicate layer, and a second gate insulating film made of the metal silicate layer and the metal oxide layer. In other words, the third inventive method for fabricating a semiconductor device is multi-gate insulating film technology in which the single layer structure of the metal silicate layer is used as a thin gate insulting film, and the multilayer structure of the metal silicate layer and the metal oxide layer is used as a thick gate insulating film. Also, in the third inventive method for fabricating a semiconductor device, a metal silicate layer with a uniform thickness and a dielectric constant higher than that of SiO2 can be formed by a reactive sputtering method or by a chemical vapor deposition method, for example, and the thickness of the metal silicate layer can be easily adjusted by controlling the sputtering conditions or the deposition conditions, for example. Accordingly, because small EOT and small leakage current can be realized in the thin gate insulating film (the first gate insulating film), increase in the gate leakage current can be prevented when the multi-gate insulating film technology is used, enabling the formation of a low-power consumption system LSI. Further, the first gate insulating film enables realizing a MOSFET in which priority is given to increase in the driving power, while the second gate insulating film enables realizing a MOSFET in which priority is given to decrease in the consumption power. As a result, a system LSI in which high driving power and low power consumption are compatible with each other can be realized.
In order to achieve the second object, a fourth inventive method for fabricating a semiconductor device includes the steps of (a) forming a metal silicate layer containing at least a first metal in a first device-formation region and a second device-formation region on a silicon substrate, and also forming a metal oxide layer containing the first metal on the metal silicate layer; (b) removing part of the metal oxide layer located in the first device-formation region, and then forming another metal oxide layer containing a second metal different from the first metal over the first device-formation region and the second device-formation region, thereby forming in the first device-formation region a first gate insulating film made of the metal silicate layer and said another metal oxide layer, and also forming in the second device-formation region a second gate insulating film made of the metal silicate layer, the metal oxide layer and said another metal oxide layer; and (c) forming a first gate electrode on the first gate insulating film, and also forming a second gate electrode on the second gate insulating film.
According to the fourth inventive method for fabricating a semiconductor device, a metal silicate layer and a metal oxide layer both containing a first metal are sequentially formed on a silicon substrate, the metal oxide layer is then partially removed, and thereafter another metal oxide layer containing a second metal different from the first metal is formed, thereby forming a first gate insulating film made of the metal silicate layer and said another metal oxide layer, and a second gate insulating film made of the metal silicate layer, the metal oxide layer and said another metal oxide layer. In other words, the fourth inventive method for fabricating a semiconductor device is multi-gate insulating film technology in which the multilayer structure of the metal silicate layer and said another metal oxide layer is used as a thin gate insulting film, and the multilayer structure of the metal silicate layer, the metal oxide layer and said another metal oxide layer is used as a thick gate insulating film. Also, in the fourth inventive method for fabricating a semiconductor device, a metal silicate layer with a uniform thickness and a dielectric constant higher than that of SiO2 can be formed by a reactive sputtering method or by a chemical vapor deposition method, for example, and the thickness of the metal silicate layer can be easily adjusted by controlling the sputtering conditions or the deposition conditions, for example. Further, in the fourth inventive method for fabricating a semiconductor device, since said another metal oxide layer is separately formed on the metal silicate layer or the metal oxide layer, said another metal oxide layer can be formed as designed without taking reaction with the silicon substrate into account. Accordingly, because the multilayer structure of the metal silicate layer and said another metal oxide layer allows small EOT and small leakage current to be realized in the thin gate insulating film (the first gate insulating film), increase in the gate leakage current can be prevented when the multi-gate insulating film technology is used, enabling the formation of a low-power consumption system LSI. Further, with the first gate insulating film, a MOSFET in which priority is given to increase in the driving power can be realized, while with the second gate insulating film, a MOSFET in which priority is given to decrease in the consumption power can be realized. As a result, a system LSI in which high driving power and low power consumption are compatible with each other can be realized.
Moreover, according to the fourth inventive method for fabricating a semiconductor device, the multilayer structure of the metal silicate layer and said another metal oxide layer, or the multilayer structure of the metal silicate layer, the metal oxide layer and said another metal oxide layer can be easily formed to have a desired thickness configuration. This enables the design of a gate insulating film in accordance with the functions called for in a MOSFET. For example, designing a gate insulating film targeted at compatibility between high driving power and lower power consumption is facilitated.
Furthermore, in the fourth inventive method for fabricating a semiconductor device, the first metal is preferably selected in such a manner that the metal silicate layer is thermally stable at the interface with the substrate and does not cause creation of great strain in the silicon crystal, which would result in deterioration of mobility in the silicon crystal. In addition, the second metal is preferably selected in such a manner that the dielectric constant of said another metal oxide layer containing the second metal is higher than the dielectric constant of the metal oxide layer containing the first metal.
In the first through fourth inventive methods for fabricating a semiconductor device, the step (a) preferably includes the step (d) of forming the metal silicate layer and the metal oxide layer by reactive sputtering in which a target containing at least the first metal is used.
It is then ensured that a metal silicate layer with a uniform thickness and a dielectric constant higher than that of SiO2 can be formed, and the thickness of the metal silicate layer can be accurately adjusted by controlling the sputtering conditions.
In the first through fourth inventive methods for fabricating a semiconductor device, the step (a) preferably includes the step (e) of forming the metal silicate layer and the metal oxide layer by chemical vapor deposition in which a source gas containing at least the first metal is used.
It is then ensured that a metal silicate layer with a uniform thickness and a dielectric constant higher than that of SiO2 can be formed, and the thickness of the metal silicate layer can be accurately adjusted by controlling the deposition conditions.
In this case, the step (e) preferably includes the step of forming the metal oxide layer in molecular strata deposited one after another by pulsed supply of the source gas.
Then, the controllability and uniformity of the thickness of the metal silicate layer can be improved.
In the first through fourth inventive methods for fabricating a semiconductor device, the first metal is preferably one metal among the group of metals consisting of Hf, Zr, Ti, Ta, Al, Pr, Nd and La, or an alloy made of two or more metals among the group of metals.
This ensures that the dielectric constant of the metal silicate layer is higher than the dielectric constant of SiO2. Also, the first metal is particularly preferably Zr in the first or third inventive method for fabricating a semiconductor device, while in the second or fourth inventive method for fabricating a semiconductor device, the first metal is particularly preferably Zr and the second metal is particularly preferably Hf.
In order to achieve the first object, a first inventive semiconductor device includes a MOSFET including a gate insulating film formed by sequentially stacking a metal silicate layer containing a first metal and a metal oxide layer containing a second metal different from the first metal.
Specifically, the first inventive semiconductor device is that formed by the second inventive method for fabricating a semiconductor device. In the first inventive semiconductor device, a gate insulating film with small EOT and small leakage current can be realized, enabling realizing a low-power-consumption MOSFET having desired driving power. It is also possible to facilitate the design of a gate insulating film in accordance with the functions called for in a MOSFET.
In order to achieve the second object, a second inventive semiconductor device includes a first MOSFET including a first gate insulating film made of a metal silicate layer containing a first metal, and a second MOSFET including a second gate insulating film formed by sequentially stacking the metal silicate layer and a metal oxide layer containing the first metal.
Specifically, the second inventive semiconductor device is that formed by the third inventive method for fabricating a semiconductor device. In the second inventive semiconductor device, increase in the gate leakage current can be prevented when the multi-gate insulating film technology is used, enabling the formation of a low-power consumption system LSI. Further, priority can be given to increase in the driving power in the first MOSFET including the first gate insulating film, while priority can be given to decrease in the consumption power in the second MOSFET including the second gate insulating film. As a result, a system LSI in which high driving power and low power consumption are compatible with each other can be realized.
In order to achieve the second object, a third inventive semiconductor device includes: a first MOSFET including a first gate insulating film formed by sequentially stacking a metal silicate layer containing a first metal and a metal oxide layer containing a second metal different from the first metal; and a second MOSFET including a second gate insulating film formed by sequentially stacking the metal silicate layer, a metal oxide layer containing the first metal, and the metal oxide layer containing the second metal.
Specifically, the third inventive semiconductor device is that formed by the fourth inventive method for fabricating a semiconductor device. In the third inventive semiconductor device, increase in the gate leakage current can be prevented when the multi-gate insulating film technology is used, enabling the formation of a low-power consumption system LSI. Further, priority can be given to increase in the driving power in the first MOSFET including the first gate insulating film, while priority can be given to decrease in the consumption power in the second MOSFET including the second gate insulating film. As a result, a system LSI in which high driving power and low power consumption are compatible with each other can be realized. In addition, it is possible to facilitate the design of a gate insulating film in accordance with the functions called for in a MOSFET.
In the first through third inventive semiconductor devices, the first metal is preferably one metal among the group of metals consisting of Hf, Zr, Ti, Ta, Al, Pr, Nd and La, or an alloy made of two or more metals among the group of metals.
It is then ensured that the dielectric constant of the metal silicate layer is higher than the dielectric constant of SiO2.
In the second or third inventive semiconductor device, the first MOSFET is preferably used in an internal circuit, while the second MOSFET is preferably used in a peripheral circuit.
It is then possible to realize a system LSI including a high-driving-power, low-power-consumption internal circuit and a low-power-consumption peripheral circuit.
In the second or third inventive semiconductor device, the first MOSFET is preferably used in a logic section, while the second MOSFET is preferably used in a DRAM section.
It is then possible to realize a system LSI including a high-driving-power, low-power-consumption logic section and a low-power-consumption DRAM section.